This disclosure generally relates to fabrics (e.g., webs or web laminates) made of thermoplastic fibers or filaments. In particular, this disclosure relates to nonwoven fabrics such as such as those produced by melt spinning thermoplastic material.
The term “nonwoven fabric”, as used herein, means a web of individual fibers, filaments, or threads that are positioned and oriented in a random manner (i.e., without an identifiable pattern). Examples of nonwoven fabrics include meltblown webs, spunbond webs, carded webs, air-laid webs, wet-laid webs and spunlaced webs and composite webs comprising two or more nonwoven layers.
The term “spunbonding”, as used herein, means a process in which filaments are formed by extruding molten thermoplastic polymer material from a plurality of fine capillaries of a spinneret, with the diameter of the extruded filaments then being rapidly reduced by drawing. Spunbond nonwoven fabrics or webs are formed by laying spunbond filaments randomly on a collecting surface such as a foraminous screen or belt. Spunbond webs can be bonded by methods known in the art such as hot-roll calendering, through air bonding (generally applicable to multiple component spunbond webs), or passing the web through a saturated-steam chamber at an elevated pressure.
Spunbond nonwoven fabrics formed from continuous bicomponent fibers are known in the art. The term “bicomponent fiber” as used herein refers to any fiber or filament (i.e., continuous or discontinuous) that is composed of two distinct polymers which have been spun together to form a single filament or fiber. Preferably each bicomponent fiber is made from two distinct polymers arranged in distinct substantially constantly positioned zones across the cross section of the bicomponent fiber and extending substantially continuously along the length of the fiber. Continuous bicomponent fibers are fibers produced by extruding two polymers from the same spinneret with both polymers contained within the same filament. Depending on the arrangement and relative quantities of the two polymers, the structure of a bicomponent fiber can be classified as core and sheath, side by side, tipped, microdenier, mixed fibers, etc.
A sheath-core bicomponent fiber comprises a core made of one thermoplastic material and a sheath made of a different thermoplastic material. The core can be concentric or eccentric relative to the sheath and can have the same or a different shape compared to that of the sheath. The sheath-core structure is employed when it is desirable for the surface of the fiber to have the property of the sheath such as luster, dyeability or stability, while the core may contribute to strength, reduced cost and the like.
Nonwoven webs can be thermally bonded using methods known in the art, including point or pattern bonding. Point or pattern bonding typically comprises the application of heat and pressure at discrete areas of the web, e.g., by passing the web through a nip formed by a patterned roll and a smooth roll or by two patterned rolls. One or both of the rolls can be heated to thermally bond the nonwoven web at distinct points, lines, areas, etc. A nonwoven fabric or web can be thermally point bonded at a plurality of spaced thermal bond points. As used herein, the term “thermal pattern bonding” refers to a process that involves passing a nonwoven fabric or web through a nip formed by a heated engraved roll and a cooperating heated smooth anvil roll. Several roll configurations (e.g., the single pass, double pass, S-wrap and three-stack idler roll configurations) are well known in the art.
Nonwoven fabrics are useful for a wide variety of applications such as surgical blankets, diapers, feminine hygiene products, towels, recreational or protective fabrics and geotextiles. In many of these applications, it is necessary for one or both surfaces of the nonwoven fabric to be abrasion resistant.
Various methods of enhancing abrasion resistance of nonwoven fabric are known. In one known method, the nonwoven fabric is passed through a nip formed by two calender rolls. Following this calendering operation, the thickness of the calendered fabric is lower than the thickness of the uncalendered fabric. Another method uses a thermal point bond calendering system (the primary bonding mechanism) with a bonding area greater than about 22%. This results in a fabric with higher stiffness. Yet another prior art method utilizes binders. This results in fabric with higher stiffness and affects the capillary action of the fabric.
Known thermoplastic, bicomponent spunbond nonwovens are either soft/silky/drapeable with very poor abrasion resistance or have good abrasion resistance without the characteristics of softness, silkiness or drapeability. Thickness is usually a good measure of drapeability. That is, for a given basis weight, the thinner the spunbond nonwoven fabric, the more compact it is, which translates to reduced drapeability.
There is a need for a method of making a nonwoven fabric having enhanced abrasion resistance without adversely impacting drapeability, capillary action and/or feel of the fabric.